Conventionally, in the steps of fabricating semiconductor devices, studies are commonly made on colloidal silica type abrasives used as chemical mechanical abrasives for smoothing inorganic insulating film layers such as SiO2 insulating films formed by processes such as plasma-assisted CVD (chemical vapor deposition) and low-pressure CVD. The colloidal silica type abrasives are produced by growing silica particles into grains by a method of, e.g., thermal decomposition of tetrachlorosilicic acid, and making pH adjustment with an alkali solution containing no alkali metal, such as ammonia. Such abrasives, however, can not provide any sufficient rate of polishing for the polishing of inorganic insulating films, and have a technical problem of low polishing rate for their practical utilization.
Meanwhile, cerium oxide abrasives are used as glass surface abrasives for photomasks. Cerium oxide particles are useful for finish mirror-polishing because they have a lower hardness than silica particles and alumina particles and hence may hardly scratch polished surfaces. Also, cerium oxide, which is known as a strong oxidant, has chemically active nature. Making the most of this advantage, its application in chemical mechanical abrasives for the insulating films is useful. However, when such cerium oxide abrasives for glass surface abrasives for photomasks are used in the polishing of inorganic insulating films as they are, they have so large a primary particle diameter as to scratch, on polishing, the insulating film surface to a visually observable extent.